Connector keying is an old art, and many forms of keying devices have been used in the past.
The need for keying electrical connectors has been long understood. Especially with multiple-contact electrical connectors, it is often necessary to prevent connecting two electrical connectors together, e.g., when in the wrong orientation or when connection to the wrong mating connector is to be avoided. Many electronic devices today utilize connectors in which the contacts are equally spaced along straight rows and are symmetrical relative to a center line of the connector. Should the plug and receptacle be reversed and coupled together, electrical connections will be made between the two connector parts, which could have catastrophic results.
Furthermore, because of intentionally imposed limitations on the number of contacts of a multi-contact connector, an electronic apparatus may be assembled with several multi-contact connectors to mate with corresponding connectors, which may be chassis mounted or printed circuit board-mounted. In these apparatuses, if the connectors are all of the same type, i.e., same number of contacts and same physical shape, the connector parts can be mistakenly inserted onto a mating connector adjacent the one intended to be connected due to the usual allowance for slack in the wiring. In other words, it is not possible under certain circumstances to prevent malfunctions due to misconnection merely by limiting the length of wire leading to the free connector part or parts.
In the prior art, one device which has been used to avoid the problems discussed above has a raised key on the outer surface of one connector part and a mating groove aligned with the key in the other connector part, with the key nesting in the groove when the connectors are properly connected. However, when more than one connector pair is used in a system, different connector parts must be chosen which have a different keying configuration of key and groove. This type of keying requires a variety of differently keyed connectors and consequently results in parts control and logistics problems. This solution to the problem is also uneconomical, involving higher costs due to the necessity of preparing many sets of expensive molds for making the connector parts.
Another prior art solution to the above-noted problem involves one of the series of female contacts of the female connector part and cutting off the male contact of the male connector part corresponding to the plugged female contact. Thus there is only one orientation of connector parts that is possible for mating, namely with the plugged female contact aligned with the cut-off male contact. Reverse orientation and incorrect selection of mating connector parts is therefore avoided. The advantage that these types of devices have over the aforementioned device is that all connector parts share a common mold. On the other hand, it is necessary to sacrifice one contact position and labor costs also increase, the contact loss can also be very disadvantageous when there is limited space within the apparatus for installing and connecting the connectors.